London - Passengers with infants were required to taste bottles of baby milk before being allowed on British flights Thursday as security measures were ramped up due to fears of a terror plot.

Police said they foiled an alleged plot to blow up flights to the United States that involved hiding explosive devices in hand baggage. Police have not confirmed media reports that liquid explosives may have been involved.

Apart from baby milk, which has to be tasted, liquids were being removed from passengers. Other measures imposed by Britain's Department for Transport included a ban on hand luggage.

The department said that all hand luggage would be put in the hold of passenger aircraft leaving the country's airports.

Passengers were being allowed to take only a limited list of items on board, ideally in a plastic bag, and nothing was being allowed on board in travellers' pockets.

Items which can be taken on board as hand luggage include:

-- pocket size wallets and size purses plus contents.

-- travel documents essential for the journey

-- prescription medicines and medical items sufficient and essential for the flight, except in liquid form unless verified as authentic.

-- spectacles and sunglasses, without cases.

-- contact lens holders, without bottles of solution.

-- for those travelling with an infant: baby food, milk (the contents of each bottle must be tasted by the accompanying passenger) and sanitary items sufficient and essential for the flight (nappies, wipes, creams and nappy disposal bags).

Passengers were being hand-searched by security staff, with all their possessions being x-rayed, including their footwear, pushchairs and walking sticks.

There was no change to security measures for hold luggage.

The Department for Transport said: "Regrettably, significant delays at airports are inevitable.

"Passengers are being asked to allow themselves plenty of extra time and to ensure that other than the few permitted items listed above, all their belongings are placed in their hold baggage and checked in.

"These additional security measures will make travel more difficult for passengers, particularly at such a busy time of the year. But they are necessary and will continue to keep flights from UK airports properly secure.

"We hope that these measures, which are being kept under review by the government, will need to be in place for a limited period only.

"In light of the threat to aviation and the need to respond to it, we are asking the travelling public to be patient and understanding and to cooperate fully with airport security staff and the police."